Time-division channel arrangement

ABSTRACT

In a packet switching system made up of a single or a plurality of switching nodes or local units each including a label conversion unit for accommodating a plurality of packet circuits and performing conversion into output port information of a switch on the basis of a logic channel on a packet circuit, a self-routing switch for performing switching on the basis of the output port information, and a control unit for terminating a control packet and performing the call processing function, and a switching node or tandem unit including a single or a plurality of self-routing switches for interconnecting the local units, there are provided a device for setting, between the tandem unit and a destination-side local unit, the same logic channel as that between an originating, side local unit operative for information transfer and the tandem unit in respect of a call destined for a local unit other than this local unit and a device, operable in the originating-side local unit for information transfer, for inserting output port information of the self-routing switch inside the tandem unit into a packet destined for the local unit other than this local unit, whereby in the tandem unit, setting of logic channel conversion information is not required to be done and even when any control signal packet from the originating-side local unit arrives at the tandem unit, the packet is transferred to the destination-side local unit without undergoing termination of packet and concomitant call processing control.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation of application Ser. No. 07/645,491, filed Jan.24, 1991 now U.S. Pat. No. 5,740,156 which is a continuation-in-part ofapplication Ser. No. 07/096,011, filed Sep. 14, 1987, now U.S. Pat. No.5,043,979.

BACKGROUND OF THE INVENTION

The present invention relates to the architecture of a packet switchingsystem having self-routing switches.

As described in "Digital Switching System" edited by The Institute ofElectronics and Communication Engineers of Japan, Mar. 15, 1986, pp.128-130, a conventional multi-processor type switching system is soconstructed as to use the function distribution and the loaddistribution in combination wherein the switching processing function isdivided into a plurality of blocks which are allotted to individualprocessors. Additional processors of the same function as that of theindividual processors are further provided in accordance with themagnitude of the load.

The function distribution faces the following problems:

(1) A fault of, for example, software in one of the processorsinfluences the whole system very greatly.

(2) The interface between processors depends on the method of dividingthe function and with loose interface, the process overhead generallytends to increase.

(3) Even the minimum scale of construction of the system has a pluralityof processors. In digital switching systems, even when load distributionis adopted in order to let one processor (unit) have completelyindependent function, such control as path setting with respect to eachcall is required in the tandem unit adapted to perform connectionbetween units, as the capacity of the system increases.

For the purpose of improving the switching throughput, the self-routingswitching system is promising being that is realizes packet switchingprocessing using a packet of fixed length, as represented by theasynchronous transfer mode (ATM), in terms of hardware. An example ofload distribution architecture of an ATM switching system usingself-routing switches is disclosed in "A Study on the Architecture ofthe ATM Switching Network", Technical Report SSE-38 of The Institute ofElectronic Information and Communication Engineers of Japan, Jul. 19,1989. However, in this example, a module for coupling distributedmodules includes a control processing for performing a packet headerprocessing, raising a similar problem to that in function distributionas described above.

In the aforementioned conventional systems, a switching unit (tandemunit) adapted to couple switching units for load distribution (localunits) must perform control for path setting in respect of each call andthe control signal must be terminated so as to carry out part of theswitching processing. This leads to problems that reliability of thetandem unit causes a bottleneck in the system and even the minimumconstruction needs the tandem unit together with the local units.

SUMMARY OF THE INVENTION

A first object of the invention is to construct a complete loaddistributed architecture in a distributed type packet switching systemby providing a local unit with an independent call processing switchingfunction and causing a tandem unit to perform only the switchingoperation by a self-routing switch without effecting any call processingcontrol corresponding to a control signal and including termination ofthe control signal.

A second object of the invention is to execute the outgoing routecontrol handling resources of the system in the above load distributedarchitecture without using the common access unit/common memory.

To accomplish the first object, according to one aspect of theinvention, a packet switching system is constructed such that an outputport of a self-routing switch inside a tandem unit is designated in anoriginating local unit; a single virtual channel (VC) is set up betweenoriginating and destination local units and a virtual channel identifier(VCI) of the VC is determined in the destination local unit; andbandwidth allotment between the local unit and tandem unit is managed bythe local unit.

To accomplish the second object, according to another aspect of theinvention, a packet switching system is constructed such that abandwidth allotment condition corresponding to an outgoing route isstored with respect to each local unit; when the bandwidth use conditionis changed, all of the other local units are informed of the change; andall of the other local units are periodically informed of the bandwidthuse condition.

When a call is originated, a start signal including a circuit bandwidthallotment condition between a call originating local unit and the tandemunit is transferred from the call originating local unit to adestination local unit and in the destination local unit, an optimumroute between local units is selected in accordance with the originatingcircuit bandwidth allotment condition and the circuit bandwidthallotment condition between the destination local unit and the tandemunit. A VCI on that circuit is hunted and a start completion signalincluding this information is returned to the originating local unit.When receiving the start completion signal, the originating local unitsets, on the basis of the selected route, output ports of individualself-routing switches inside the originating local unit, tandem unit anddestination local unit in a label conversion table, and adds thisinformation to a subsequently transferred user information packet.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram showing a packet switching systemaccording to an embodiment of the invention;

FIG. 2 is a block diagram of a packet line interface;

FIGS. 3, 4 and 19 show label conversion tables;

FIG. 5 is a block diagram showing an example of construction of a localunit;

FIGS. 6A to 6C show packet formats;

FIG. 7 is a diagram showing the routing architecture between originatingand destination local units;

FIG. 8 is a signal sequence diagram;

FIG. 9 is a transmission processing flow chart;

FIGS. 10 and 11 show route management tables;

FIG. 12 is a termination processing flow chart;

FIG. 13 is a start completion processing flow chart;

FIG. 14 is a diagram showing outgoing route selection sequence;

FIG. 15 is a destination unit determining processing flow chart;

FIG. 16 is an outgoing call termination analysis processing flow chart;

FIG. 17 is a release processing flow chart;

FIG. 18 is a schematic block diagram showing an integrated node systemaccording to another embodiment of the invention; and,

FIG. 20 is a schematic block diagram showing a packet switching systemcomprising local units alone according to still another embodiment ofthe invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A preferred embodiment of the invention will now be described withreference to the accompanying drawings.

1. Explanation of Construction

1.1 Construction of Switching System

FIG. 1 shows an example of construction of a self-routing packetswitching system to which the invention is applied. This switchingsystem comprises k local units (1-1 to 1-k) each accommodating n packetcircuits, and a single tandem unit 2 coupled to the local units. Eachlocal unit 1 includes a self-routing switch 3 for switching a packetthrough self-routing operation, a signal processor 5 for processingcontrol signals, a central controller 6 for managing call processingcontrol and call resource, and line interfaces 7 for performing linetermination, such as optoelectric conversion, synchronous control andlabel conversion. The tandem unit 2 includes a plurality of self-routingswitches (4-1 to 4-p). Each local unit 1 and the tandem unit 2 arecoupled together by packet circuits (9-1 to 9-q) between desiredoriginating and destination local units, a plurality of routes runthrough the self-routing switches (4-1 to 4-q) in the tandem unit 2.

It is to be noted that the construction of FIG. 1 is an improvementbased on U.S. Pat. No. 5,043,979 assigned to the same assignee of thepresent application. The relation between the FIG. 1 construction andthe U.S. Pat. No. 5,043,979 (hereinafter referred to as a prior patent)will be described herein.

Firstly, the local units (1-1 to 1-k) in FIG. 1 of the present patentcorrespond to front-end modules FM (201 to 208) in FIG. 1 of the priorpatent, and the tandem unit 2 of the present application corresponds tocentral module CM 100 of the prior patent. In the prior patent, the FM'sare described as being sorted into SM's connected to subscriber linesand TM's connected to trunk lines but the SM and TM have substantiallythe same construction. Also, while in the prior patent, the FM's aredescribed as being sorted into up-FM's and down-FM's (for example, FM's201 and 203), up- and down-FM's in the present application are describedas being incorporated in one block (for example, local unit 1-1), thatis, the up-and down-FM's are described as being disposed on the sameside in one block with respect to the tandem unit, but the substance isthe same for the prior and present applications.

Further, process/control unit 405 (FIG. 6) in the front-end module FM ofthe prior patent corresponds to the signal processor (5-1 to 5-k) andcentral controller (6-1 to 6-k) in FIG. 1 of the present applicationwhich are adapted to perform idle/busy management of circuits and callcontrol. Differently, however, in the present application, therespective self-routing switches (3-1 to 3-k) are incorporated in therespective local units (1-1 to 1-k).

In addition, the format in FIG. 4 of the prior patent corresponds tofixed-length blocks (cells) to be described later with reference toFIGS. 6A to 6C of the present application.

1.2 Construction of Line Interface

The line interface 7 has a circuit construction as shown in FIG. 2.Interfaces 7a and 7b respectively include an up-circuit 21 and adown-circuit 22, the up-circuit being operable to process a packet on anincoming circuit 8a of the switching system (this incoming circuitcorresponds to a subscriber line or a trunk line between the system ofinterest and another network system) or a packet on an incoming circuit9b (this incoming circuit corresponds to an incoming circuit betweenunits) to deliver the processed packet to a packet circuit 10a or 262aconnected to the self-routing switch 3-1 in the local unit 1-1, and thedown-circuit being operable to process a packet on an outgoing circuit10b or 262b to deliver the processed packet to an incoming circuit 8b or9a. As the common function components, the up-circuit 21 has anoptoelectric (O/E) converter 31 for optoelectric conversion and asynchronous circuit 32 for synchronous control and the down-circuit 22has an electrooptic (E/O) converter 31 for electrooptic conversion and asynchronous circuit 32. In the up-circuit 21, the incoming circuit 8a(9b) then connects to an input register 25 and to an output register 24through a delay circuit 23. A line 27 for taking out a virtual channelidentifier (VCI) leads from the input register 25 and the taken-out VCIserves as a read address for a label conversion table 26. A data outputline 28 leading from the label conversion table 26 connects to theoutput register 24 and the outgoing circuit 10a of the output register24 connects to the tandem unit 2.

1.3 Label Conversion Table

FIG. 3 shows a label conversion table in the line interface 7a connectedto the switching system incoming circuit 8 and FIG. 4 shows a labelconversion table in the line interface 7b connected to the circuit 9between the local and tandem units. The conversion table of FIG. 3 isdivided into a VCI area for control signal and a VCI area for userinformation and in respect of a VCI on the incoming circuit 8a (VCIi),the conversion table is set with a VCI on a circuit between the tandemunit and a destination local unit (this VCI is termed IVCI), an outputport number PT1 of self-routing switch 3 in an originating local unitand an output port number PT2 of self-routing switch 4 in the tandemunit.

The label conversion table of FIG. 4 is also divided into a controlsignal area and a user information area as in the precedence and inrespect of an IVCI on the incoming circuit 9b from the tandem unit 2, itis set, in its control signal area, with an outgoing circuit control VCI(VCIoc), an outgoing circuit control virtual path identifier (VPI) or(VPIoc) and an output port number PT of self-routing switch 3 in adestination local unit 3 and, in its user information area, with anoutgoing circuit user information VCI (VCIou), an outgoing circuit userinformation VPI (VPIou) and a PT.

1.4 Construction of Self-routing Switch

The self-routing switch 3 or 4 is packet switch operable to select anoutgoing circuit in accordance with output port information in a packetand may be constructed of either a single switch or a plurality of unitswitches.

The self-routing switch 3 in the local unit is constructed as shown inFIG. 5, including an up-circuit unit self-routing switch 51a receivingthe output line 10a of the line interface (7a-1 to 7a-n) connected withthe incoming circuit (8a-1 to 8a-n) and a down-circuit unit self-routingswitch 51b receiving the outgoing circuit 262a of the line interface(7b-1 to 7b-n) connected with the circuit (9b-1 to 9b-q) from the tandemunit. The up-circuit unit self-routing switch 51a has output lines(262b-1 to 262b-q) connected to the line interface 7b connected with thetandem unit 2, and the down-circuit unit self-routing switch 51b hasoutput lines (10b-l to 10b-n) connected to the line interface (7a-1 to7a-n).

The up-circuit unit self-routing switch 51a connects to an up-circuitsignal processor 53 and the down-circuit unit self-routing switch 51bconnects to a down-circuit signal processor 52, the signal processorsbeing connected to the central controller through a processor bus 29.

1.5 Structure of Packet Format

FIGS. 6A, 6B and 6C show structures of packet formats on differentcircuits. A packet is divided into a header field and a user field andthe header field contains a VCI area and a VPI area. As shown in FIG.6A, a packet format on the incoming circuit 8a to an originating localunit has an incoming circuit VCI (VCIi) and an incoming circuit VPI(VPIi) which are set in its packet header field. FIG. 6B shows a packetformat on a circuit between a line interface (for example, 7a-1) of theoriginating local unit 1-1 and a line interface (for example, 7'b-1) ofa destination local unit (for example, 1-K), that is to say, forexample, the circuit 10 between line interface 7a and self-routingswitch 3 and the circuit 9 between local unit 1 and tandem unit 2. Inthe packet format of FIG. 6A, an IVCI is set in the VCIi area and anoutput port number PT1 of self-routing switch 3-1 of the originatinglocal unit 1-1 and an output port number of self-routing switch 4 of thetandem unit 2 are set in the VPIi area. As shown in FIG. 6C, a packetformat on an outgoing circuit 8b of the destination local unit 1-k isset with an outgoing circuit VCI (VCIo) and an outgoing circuit VPI(VPIo).

1.6 Construction of Integrated Node System

FIG. 18 shows an example of the construction wherein the previouslydescribed packet switching system is added with the ATM cross connectingfunction. The tandem unit 2 with the self-routing switches (4-1 to 4-p)operable for connection between local units is additionally providedwith a self-routing switch (255) for cross connecting which is connectedto an ATM trunk network 251. The cross connecting self-routing switch(255) is coupled to a single or a plurality of local units through apacket circuit 9 and is also coupled to the ATM trunk network 251through a packet circuit 250. Each self-routing switch (4-1 to 4-p; 255)in the tandem unit 2 is preceded by up-circuits 256 of line interface.The up-circuit 256 in FIG. 18 has the construction resembling the block21 of FIG. 2 and its input register takes out a VPI from the cell headerto deliver the VPI to the label conversion table 26. Further, a signalprocessor 252 for initialization of the label conversion table and acentral controller 253 are provided in association with eachself-routing switch.

FIG. 19 shows a structure of the label conversion table 26 in the lineinterface of the tandem unit 2. In accordance with a VPI (VPIi) on theincoming circuit (9a; 250a), an output port number PT of theself-routing switch (4; 255) and a VPI (VPIo) on the correspondingoutgoing circuit (9b; 250) are set.

Thus, the packet format on the incoming circuit 8 connected to theterminal is shown in FIG. 6A, the packet format on the circuit 9 betweenthe local and tandem units is shown in FIG. 6B and the packet format onthe circuit 250 between the ATM trunk network 251 and tandem unit 2 isshown in FIG. 6C.

2. Explanation of Operation

From the standpoint of connection destination, calls handled by theswitching system may be classified into a call to be terminated at astation of interest (i.e this station), which call is destined for thisstation and a call to go out to another station, which call leaves astation for a different station.

2.1 Call to Be Terminated at This Station

The call to be terminated at this station is sorted into a call insidethis station which is originated from a terminal inside this station andan incoming connection call standing for a call which is originated fromanother station and destined for this station. Here, the invention willbe described by way of a call inside this station.

FIG. 7 shows an example wherein a call originated from a terminal 61connected to the local unit 1-1 is destined for a terminal 62 connectedto the local unit 1-k. The local unit 1-1, the local unit 1-k, theterminal 61 and the terminal 62 will hereinafter be termed anoriginating local unit, a destination local unit, an originatingterminal and a destination terminal, respectively. The route fortransfer of control signal information between the originating anddestination terminals is fixedly allotted (in this example, allotted toroute 1) and the user information transfer route is selected from routes1 to p.

Following the origination of a call by the originating terminal 61, theswitching system operates as will be described with reference to FIG. 8.

[Transmission Processing]

An origination call signal packet from the originating terminal isinputted to the line interface 7 through the incoming circuit 8a inFIG. 1. At that time, the packet format is as shown in FIG. 6A and set,in its VPIi area, with a control signal VPIic and, in its VCIi area,with a user information VCIic. Turning to FIG. 2, the VCI area of thepacket header field is separated from the input register 25 and itsvalue, VCIic, appearing on the data line 27 accesses the labelconversion table 26. In the conversion table 26 as detailed in FIG. 3,an IVCI and PT information are set in an address (control signal area)corresponding to the control signal VCIic. As the IVCI, a value allottedin correspondence to the incoming circuit number is fixedly set and asPT1 of the PT information, an outgoing circuit number of a unitself-routing switch 51a connected with a signal processor (for example,53 in FIG. 5) in the originating local unit 1-1 is set. (PT2 and PT3 arenot used here.) The IVCI and PT information are produced on the dataline 28 and delivered to the output register 24 where they are insertedin the packet header field. In this phase, the packet format is as shownin FIG. 6B. This packet is inputted to the up-circuit self-routingswitch 51a of FIG. 5 through the circuit boa and switched to the signalprocessor 53 in accordance with PT1 in the packet header. The signalprocessor 53 then performs signal processings such as packet assemblyprocessing and link access procedure on the D-channel (LAPD) andthereafter a transmission analysis program 91 as shown in FIG. 9 isstarted in the central controller 6.

In the transmission analysis program 91, a number (receiving number)dialed by the originating terminal 61 and contained in the originatingcall is translated to determine the destination local unit 1-k (100).Then, an originating-side-route idle/busy table of FIG. 10 whichindicates the idle/busy state in terms of one bit in respect of theroutes (routes 1 to p) between local units (in this example, 0/1corresponds to busy/idle) is read to detect an idle route (101).Subsequently, a use bandwidth corresponding to the idle route is readout of an originating-side-route use bandwidth management table and theread use bandwidth is added with a user notified bandwidth contained inthe originating call signal (102). Thus, in respect of a route for whicha bandwidth resulting from the addition exceeds an allotment limitvalue, idle indication is changed to busy indication (103) and a startsignal having as parameters a bit pattern indicative of the idle/busy ofthe route and the user notified value is transmitted to the tandem unit(104).

The start signal is transferred from the central controller 6 to theup-signal processor 53 where the start signal is decomposed into apacket, the packet header of which is set with PT1 and PT23corresponding to the route 1 (FIG. 7) fixedly allotted in correspondenceto the destination local unit 1-k. In accordance with the routinginformation in the packet header, this start signal arrives at the lineinterface 7'b of the destination local unit 1-k through the self-routingswitch 3-1 of originating local unit 1-1 and the self-routing switch 4-1of the tandem unit. In the line interface 7'b, the label conversiontable as shown in FIG. 4 has the control signal area from which outgoingcircuit VCIoc and VPIoc and an output port number PT of the self-routingswitch 3-k to which the signal processor 5-k is connected are read andinserted into the header field. In accordance with the PT information,the packet is so switched by the self-routing switch 3-k as to bedestined for the signal processor 5-k of FIG. 1 in the destination localunit 1-k (corresponding to the down-packet signal processor 52 in FIG.5).

[Termination Processing]

When the start signal arrives at the destination local unit, the programproceeds as follows. In the signal processor 52 receiving the startsignal, signal processings such as packet assembly and LAPD are carriedout as in the processing in the originating local unit and thereafter atermination analysis program 92 in the central controller 6 is started.A process flow of the termination analysis program 92 is shown in FIG.12. Firstly, a route which is allowed to be allotted between thedestination local unit 1-k and the tandem unit is selected (120). Inthis processing, as in the case of the originating route selection, adestination-side route idle/busy table (corresponding to FIG. 10) whichindicates the idle/busy state in terms of one bit in respect of eachroute is read so that an idle route may be detected. Subsequently, a usebandwidth corresponding to the idle route is read out of adestination-side-route use bandwidth management table and the read usebandwidth is added with a user notified bandwidth contained in the startsignal. Thus, in respect of a route for which a bandwidth resulting fromthe addition exceeds an allotment limit value, idle indication ischanged to busy indication and a bit pattern indicative of the idle/busyof the destination-side route is determined. The destination-sideidle/busy bit pattern and the originating-side idle/busy bit pattern inparameters of the start signal are AND-ed to select an idle route (121).Then, a use bandwidth of the selected route in the destination-routebandwidth management table is renewed in accordance with the usernotified value (122). When the renewed result reaches an allotment limitvalue, the destination-side-route idle/busy table is also renewed fromidle to busy. After a user information IVCIu on the selected route ishunted (123), an accommodation position of the destination terminal 62is determind in accordance with a reception number in the receivedpacket (124) and a circuit PT connected to the destination terminal andVPIou and VCIou on the channel are hunted (125). The VPIou, VCIou and PTare set in an area (user information area) corresponding to IVCIu of alabel conversion table in the destination local unit 1-k through theprocessor bus 29 coupled to the central controller (126). Thereafter astart completion signal having as parameters the user notified value,route permissible for allotment (the route determined in step 121) andhunted IVCIu is transmitted to the originating local unit (127). Likethe start signal transmission processing in the originating local unit,the start completion signal transmission processing is such that thesignal packet is transferred from central controller 6 to signalprocessor 53 and in this signal processor 53, the signal packet isdecomposed into a packet, the packet header of which is set with PT1 andPT2 corresponding to the route 1 fixedly allotted in correspondence tothe originating local unit 1-1. In accordance with the routinginformation in the packet header, this start completion signal arrivesat the self-routing switch 3-k of destination local unit 1-k, theself-routing switch 4-1 of tandem unit 2 and the line interface 7b oforiginating local unit 1-1. In the line interface 7b, the labelconversion table as shown in FIG. 4 has the control signal area fromwhich outgoing circuit VCIoc and VPIoc and an output port number PT ofthe self-routing switch 3-1 connected with the signal processor 5-1 areread and inserted in the header field. In accordance with the PTinformation, the packet is so switched by the self-routing switch 3-1 asto be destined for the signal processor 5-1 of FIG. 1 in the destinationlocal unit 1-k (corresponding to the down-packet signal processor 52 inFIG. 5).

[Start Completion Processing]

When the start completion signal arrives at the originating local unit,the program proceeds as follows. In the signal processor 52 (FIG. 5)receiving the start signal, signal processings and packet assembly arecarried out and thereafter a start completion processing program 93 inthe central controller 6 is started. A flow chart of the startcompletion processing program 93 is shown in FIG. 13. Theoriginating-side-route use bandwidth management table of FIG. 11 isrenewed in respect of an allotted route in parameters of the signal(140). VPIiu and VCIiu on the circuit connected to the originatingterminal 61 (FIG. 7) are hunted (141). Parameter IVCIu in the startcompletion signal and the output port information PT1, PT2 are set in anarea (user information area), corresponding to the VCIiu, of the labelconversion table through the processor bus 29 coupled to the centralcontroller. The output port information is determined in accordance withthe route between the originating and destination local units.

Through the above procedure, the call setting processing is completed.

[Upon Transfer of Information]

Following call setting, a user information packet 78 from theoriginating terminal 61 and having in its packet header of VPIiu andVCIiu arrives at the originating local unit 1-1. The operation in thisphase will now be described.

In the up-circuit 21 of FIG. 2, the VCI area of the packet header fieldis separated from the input register 25 and its value, VCIic, appearingon the data line 27 accesses the incoming-side label conversion table26. In the incoming-side conversion table 26 as detailed in FIG. 3, theIVCIu hunted upon call setting and the selected output port informationPT1, PT2 are set in an address corresponding to the user informationVCIiu. The IVCIiu and the PT information are sent through the data line28 to the output register 24 where they are inserted in the packetheader field. This packet is sent through the circuit 10-a to theself-routing switch 3-1 by which it is switched in accordance with thePT1 in the packet header so as to be transferred to the tandem unit 2through a circuit, for example, 9a-q. In the tandem unit 2, the packetis then switched by self-routing switch 4-q in accordance with the PT2in the packet header so as to arrive at the line interface 7'b-1 in thedestination local unit 1-k through the circuit 9'b-1. In the up-circuit21 of FIG. 2, the VCI area of the packet header field is separated fromthe input register 25 and its value, IVCIu, appearing on the data line27 accesses the label conversion table 26. In the conversion table 26,circuit PT connected with the destination terminal 62 and VPIou andVCIou on that circuit are set in an address corresponding to the userinformation IVCIu. The circuit PT and VPIou and VCIou are sent throughthe data line 28 to the output register 24 where they are inserted intothe packet header field. In accordance with the PT in the packet header,this packet is so switched by the self-routing switch 3-k in thedestination local unit 1-k as to be destined for a line interfaceconnected to the destination terminal, for example 7'a-1. The userinformation packet with the inserted VPIou and VCIou arrives at thedestination terminal 62 through an outgoing circuit 8'b-1.

2.2 Call to go out to Another Station

An outgoing call destined to another station is sorted into an outgoingcall which is originated from a terminal of this station and a tandemcall which is originated from another station and arrives at thisstation. The following description will be given by way of the outgoingcall transmitted from this station.

[Sequence of Selection of Outgoing Route]

Typically, a switching system is connected with a plurality of outgoingroutes (routes running to another switching system) and in accordancewith a result of translation of a received dial number, one of theoutgoing routes is selected and a necessary bandwidth is assigned on theselected route. If the assignment fails, a necessary bandwidth isreassigned on a predetermined by-pass route. The route to be selectedinitially is called a first route and the by-pass route is called asecond route.

In a distributed type switching system in which a plurality of localunits exist, when a plurality of circuits are to be accommodated in thesame route from a switching system, the circuits are accommodated bydistributing each of the first and second routes to a plurality of localunits as shown in FIG. 14, in consideration of risk deconcentration.

In respect of a call originating from a terminal 150 in a local unit 151shown in FIG. 14, a route is selected in accordance with the followingsequence.

(1) A first route for accommodating this local unit 151 is selected.

(2) If the above route in (1) is busy, a first route for accommodatinganother local unit (for example, 152) is selected.

(3) If the above route in (2) is busy, a second route for accommodatingthis local unit 151 is selected.

(4) If the above route in (3) is busy, a second rote for accommodatingthe second local unit (for example, 152) is selected.

<Transmission Processing>

Like the call to be terminated at this station, control is carried outin accordance with the signal sequence shown in FIG. 8.

In connection with outgoing calls, the destination unit determining step100 in the transmission analysis program 91 of FIG. 9 determines a unitin which a route determined pursuant to the route selection sequence isaccommodated, in accordance with a processing flow as shown in FIG. 15.Number translation tables 180 and 181 are retrieved by a received numberto perform outgoing call identification so that a VPI corresponding toan outgoing route number may be read (170). It is checked whether theVPI is permissible for allotment to the VP in this local unit (171) andif permissible, a connection is done which is closed inside this localunit. If the allotment is impermissible or a circuit of interest is notconnected to this local unit, a bandwidth use condition corresponding tothe VPI is read out of an outgoing call management table 182 (172). Forexample, the bandwidth use condition is expressed by two bits in respectof each unit, with value "0" indicating non-use, value "1" indicating alow use condition (lower than a threshold), value "2" indicating a highuse condition (higher than the threshold) and value "3" indicating busy(also indicative of non-packaging). In accordance with the bandwidth usecondition, a unit permissible for allotment is selected (173). If allthe units are impermissible for allotment, a by-pass table 183 is usedand a by-pass route (next VPI) is read therefrom (174) and thenprocessings (steps 171 to 175) like those in the aforementioned firstroute are carried out. If no by-pass route is available in the by-passroute table 183, a blocking processing is effected (175). When adestination local unit is determined, selection step 105 of routebetween the originating and destination local units, as shown in FIG. 9,is carried out as in the case of the call to be terminated at thisstation. The originating-side-route idle/busy table of FIG. 10 whichindicates the idle/busy state by one bit in respect of each route (inthis example, 0/1 corresponds to busy/idle) is read to detect an idleroute (101). Subsequently, a use bandwidth corresponding to the idleroute is read out of the originating-side-route use bandwidth managementtable shown in FIG. 11 and added with a user notified bandwidthcontained in the originating call signal (102). Thus, idle indication ischanged to busy indication in respect of a route in which the additionresult exceeds an allotment limit value (103), and a start signal havingas parameters a bit pattern indicative of route idle/busy and the usernotified value is transmitted to the tandem unit (104).

<Termination Processing>

When the start signal arrives at the destination local unit, an outgoingcall termination analysis program 92 as shown in FIG. 16 is started. Apresently used bandwidth of the designated VPI contained in theparameter of the start signal is read out of an outgoing route usebandwidth table 196 (190) and it is checked whether allotment ispermissible (191). If the allotment is impermissible, a startincompletion signal is returned to the originating local unit (194) butif permissible, the outgoing route use bandwidth table 196 is renewed.If as the result of the allotment the threshold in the outgoing callmanagement table 182, predetermined upon call setting, is exceeded, anoutgoing route control signal having as parameter the changed value istransmitted to all of the other units (195). Thereafter, the processinglike the termination analysis 92 of the call to be terminated at thisstation is effected. A route permissible for allotment between thedestination local unit 1-k and the tandem unit is selected (120). Inthis processing, as in the case of the originating-side route selection,the destination-side-route idle/busy table (corresponding to FIG. 10)which indicates the idle/busy state by one bit in respect of each routeis read to detect an idle route. Subsequently, a use bandwidthcorresponding to the idle route is read out of thedestination-side-route use bandwidth management table corresponding toFIG. 11 and added with a user notified bandwidth contained in the startsignal. Thus, idle indication is changed to busy indication in respectof a route in which the addition result exceeds an allotment limit valueand a bit pattern indicative of the idle/busy of thedestination-side-route is determined. The destination-side idle/busy bitpattern and the originating-side idle/busy bit pattern in parameters ofthe start signal are ANDed to select an idle route (121). Then, a usebandwidth of the selected route in the destination-route bandwidthmanagement table is renewed in accordance with the user notified value(122). When the renewed result reaches an allotment limit value, thedestination-side-route idle/busy table is also renewed from idle tobusy. After a user information IVCIu on the selected route is hunted(123), a circuit PT connected to the destination terminal 62 isdetermined in accordance with a reception number in the received packet(124) and VPIou and VCIou on the circuit connected to the destinationterminal are hunted (125). The VPIou, VCIou and PT are set in an area(user information area) corresponding to IVCIu of a label conversiontable in a line interface of the destination local unit through theprocessor bus 29 coupled to the central controller (126). Thereafter astart completion signal having as parameters the user modified value,route permissible for allotment (the route determined in step 121) andhunted IVCIu is transmitted to the originating local unit (127).Subsequently, a call is set as in the case of the call to be terminatedat this station and the user information is transferred.

<Release Processing>

Upon release of a call, a release processing program as shown in FIG. 17in the central controller of the destination local unit is started inresponse to a disconnection signal from the partner station. Theoutgoing route use bandwidth table 196 is renewed (subtraction) (201),each call resource is released (202) and a release signal is transmittedto the originating local unit (203). Following the call releaseprocessing, it is checked in the outgoing call management table 182whether a predetermined threshold for release is exceeded (204) and ifexceeded, an outgoing route control signal having a changed value asparameter is transmitted to all of the other units (205).

<Notification Processing>

Exemplarily, in the foregoing embodiment, the use bandwidth is checkedfor its change in respect of each call and when a predeterminedthreshold is exceeded, an outgoing route control signal is transmittedbut there is available a system wherein checking is not done in respectof each call but each local unit periodically informs all of the otherunits of the use condition. In such a system as above, an outgoing routeinformation transfer program is provided in the central controller ofthe local unit and started periodically, whereby the use condition ofeach VPI in this local unit is checked and an outgoing route controlsignal having as parameter, for example, a 2-bit value to be set in theoutgoing call management table 182 is transmitted.

2.3 Call Operation in Integrated Node Architecture

Call operation in an integrated node system as shown in FIG. 18 will nowbe described. An ATM network 251 has such a construction that thephysical link, virtual path VP and virtual connection VC betweenswitching systems (nodes) are set up hierarchically. In the systemconstruction shown in FIG. 18, the above hierarchical networkconstruction is applied among the circuit 250 connected to the ATMnetwork 251, the local switch 1 and the ATM cross-connector,self-routing switch 255. Similarly, the aforementioned hierarchicalnetwork construction is also set up among circuits, generally designatedby reference numeral 9, between the local unit and the tandem unit.Accordingly, the originating local unit assigns a VPI between theoriginating local unit and tandem unit to a packet delivered to thetandem unit 2 and in the tandem unit 2, the VPI (VPIi) is converted, inthe label conversion table 256 preceding the self-routing switch (4;255), into a VPI (VPIo) between the destination unit and tandem unit andan output port number PT of the self-routing switch (4; 255).

The call passing through the tandem unit 2 is sorted into three kindsconsisting of a call between local units which runs through theself-routing switches 4-1 to 4-p as described in the foregoingparagraphs 2.1 and 2.2, an outgoing (incoming) call which uses forcross-connection the self-routing switch 255, and a trunk call whichcauses a call from the trunk network 251 not to be terminated at thisstation but to be passed again through the trunk network 251.

(1) Call between Local Units

This call runs through the self-routing switches 4-1 to 4-p forinterconnection of local units in the tandem unit 2 and with this call,in the originating local unit, the output port number RT of theself-routing switches 4-1 to 4-p in the tandem unit 2 is not designatedbut a VPIi between the originating local unit and tandem unit isdesignated (inserted into a packet), whereby in the label conversiontable 256 of the tandem unit 2, the VPIi is converted into a VPIobetween the destination local unit and tandem unit and an output portnumber RT of the self-routing switches 4-1 to 4-p, thus effecting thecall operation described in the foregoing paragraphs 2.1 and 2.2

(2) Outgoing (Incoming) Call

This call runs between this node and the trunk network 251 through theself-routing switch 255 for cross-connection in the tandem unit 2 andconsists of an outgoing call which leaves this node for the ATM trunknetwork 251, and an incoming call which is destined from the ATM trunknetwork 251 for this node. Here, the outgoing call will be described.

Through the call setting operation described in paragraph 2.2, userinformation is transferred in sequence of the originating local unit(for example, 1-1), self-routing switch inside the tandem unit (forexample, 4-1) and destination local unit (for example, 1-k) and it istransmitted, in the form of a packet format shown in FIG. 6C, to apacket circuit 9' a-s connected to the self-routing switch 255 forcross-connection inside the tandem switch 2. In the label conversiontable 256 connected to the packet circuit 9' a-s in the tandem switch 2,VPIo is converted into a VPI for ATM trunk network 251 and an outputport number PT of the self-routing switch 255 for cross-connection,which information is inserted into the packet header. In theself-routing switch 255, the packet is switched in accordance with thePT so as to be transmitted to a packet circuit connected to the ATMtrunk network 251 (for example, 250b-1).

(3) Trunk Call

This call is to cause a call from the trunk network 251 not to arrive atthe packet switching system but to pass again through the trunk network251 by using the self-routing switch 255 for cross-connection inside thetandem switch 2 and with this call, this node is used as only an ATMcross-connector. A packet from the ATM trunk network 251, in the form ofa packet format shown in FIG. 6C, arrives at the tandem switch 2 througha packet circuit 250a-u, for example. Then, as in the case of theoutgoing call, the packet is transferred to a packet circuit (forexample, 250b-1) connected to the ATM trunk network 251.

The signal processor 252 and central controller 253 are not used upontransfer of information but are used upon setting of label conversiontable. When building station or extending station, the local unit 1transmits as a table rewrite request signal a control packet using aspecial VPI to the tandem unit 2 and the label conversion table 256 inthe tandem unit delivers an output port number PT of a circuit connectedto the signal processor 252 so that the control packet may terminate atthe signal processor 252. The signal processor assembles a packet andinforms the central controller 253 of the assembly of the packet. Inaccordance with a parameter of the signal, the central controller 253sets the label conversion table 256.

A packet switching system comprised of only local units according toanother embodiment of the invention will now be described with referenceto the accompanying drawing.

1. Explanation of Construction

1.1 Packet Switching System Comprised of Only Local Units

FIG. 20 shows an example of construction of a packet switching systemcomprising a plurality of local units. Circuits between the local unitsdo not run through a tandem unit but direct interconnection in a meshpattern is established between local units. In the constructionalexample of FIG. 20, an inter-local unit circuit group 301 connects alocal unit 1-1 and a local unit 1-3, an inter-local unit circuit group302 connects the local unit 1-1 and a local unit 1-2, and an interlocalunit circuit group 303 connects the local unit 1-2 and a local unit 1-3.

2. Explanation of Operation

2.1 Call Operation of System Comprised of Only Local Units

Call operation in the packet switching system (FIG. 20) comprising aplurality of local units will now be described. Since the inter-localunit circuit does not run through a tandem unit but direct inter-localunit connection is established, negotiation between the originating anddestination local units can be dispensed with when selecting a circuitbetween local units. This is because it will do that any one of thelocal units, for example, only the originating local unit may manage theinter-local unit circuit. Accordingly, the transmission analysisprocessing 91 of FIG. 9 can dispense with steps 103 and 104 and in aresulting processing, an inter-local unit circuit is hunted. Similarly,the termination analysis processing 92 of FIG. 12 may be removed ofsteps 120, 121 and 122 and the start completion processing 93 of FIG. 13may be removed of step 140.

As is clear from the foregoing description, by adopting the completeload distributed construction wherein each local unit is allowed to havethe independent switching function and control in respect of each callis not carried out in the tandem unit, the following effects can beobtained.

(1) Even in the event that a fault occurs in the tandem unit or acircuit between the local unit and the tandem unit, stand-aloneoperation can be permitted for a call which returns inside the localunit.

(2) By making communications between the local unit and tandem unit aninter-station interface, the use of standard units and standard programscan be permitted.

(3) The minimum construction can be of a single local unit alone,offering advantages of high economy and high extension capability forenlargement of scale.

Further, by managing a use bandwidth of a circuit between the local unitand tandem unit by means of the local unit connected with that circuitand selecting an optimum route by taking the bandwidth use condition ofthe destination circuit into consideration in accordance with a controlsignal upon call setting, the call loss rate can be decreased ascompared to the system in which the route is selected by means of onlythe originating local unit.

Further, by hunting a VCI at a destination-side local unit to whichinformation is transferred, unique allotment of VCI to calls incomingfrom a plurality of local units and being multiplexed on the samecircuit can be ensured so that the call can be identified by only theVCI. Accordingly, the address amount of the label conversion conformableto only the VCI sufficies and as compared to the case where theoriginating unit is also taken into consideration to allot the address,the memory amount can be decreased by 1/n in a system accommodating nlocal units.

Further, by making it possible to effect, in this complete distributedconstruction, the control of the outgoing call handling the commonresource of the system, superiority can be ensured over the systemprovided with the common resource server, from the standpoint ofperformance such as spread of fault and call delay time.

In addition, by incorporating the ATM connector function into the tandemswitch, the maintenance/working such as extension, which has hithertobeen effected independently in respect of the switchingsystem/transmission system can be realized through the same operation.

We claim:
 1. A distributed type switching system, comprising:a pluralityof local units, each being connected to a plurality of externalcircuits, for transmitting and receiving packets on said externalcircuits, each of said packets including a header and an informationfield, each of said local units including at least one first selfrouting switch for self routing packets to and from said externalcircuits connected to local unit based on output port information; and atandem unit including at least one second self-routing switch forinterconnecting said local units by self-routing packets to and fromsaid local units based on output port information; each of said localunits further including a plurality of header converters each for addingsaid output port information for said first self routing switch of thelocal unit and said second self routing switch of said tandem unit, tothe header of a packet received from one of said external circuitsconnected to the local unit and means for storing a bandwidth allotmentstate of outgoing routes of the local unit to permit a call originatinglocal unit to determine whether a call is permissible on an outgoingroute of the local unit.
 2. A distributed type switching systemaccording to claim 1 wherein when said call is determined not to bepermissible on said outgoing route of said local unit, said calloriginating local unit selects a local unit having an outgoing route onwhich said call is permissible.
 3. A method in a distributed typeswitching system having a plurality of local units, each being connectedto a plurality of external circuits, for transmitting and receivingpackets to and from said external circuits, each packet includes aheader and an information field, and a tandem unit for interconnectingsaid local units, said method comprising the steps of:adding routinginformation to a header of a packet received from one of said externalcircuits by one of said local units to indicate a destination of saidpacket within said switching system; self routing said packet by saidlocal unit and said tandem unit to reach said destination based on saidrouting information; and storing a bandwidth allotment state of outgoingroutes of said local unit to permit a call originating local unit todetermine whether a call is permissible on an outgoing route of saidlocal unit.